A bar worker at a popular Times Square karaoke club was arrested Thursday after confessing to beating a woman to death with a pipe on the club's roof during an argument, police said.

Syed Rahman, 24, admitted he smashed Ingrid Rivera over the head at about 2:45 a.m. Monday during a birthday party for rapper Lil' Kim that the victim had paid to attend, Police Commissioner Raymond Kelly said at a news conference. Her body was discovered Wednesday afternoon.

It was unclear what Rahman and Rivera, who had met for the first time inside Spotlight Live club that night, were arguing about. But a friend of Rivera pointed police to Rahman by telling them she had fought off his sexual advances on the roof shortly before the slaying, Kelly said.

Rahman -- who had worked at the club for four years and had no previous criminal record -- was arrested on a charge of second-degree murder, which carries a penalty of up to life in prison upon conviction. Authorities did not have the name of his lawyer.

The medical examiner ruled the death a homicide Thursday after an autopsy found that the 24-year-old Rivera died from a blow to the head.

Police said Rivera was a Lil' Kim fan who arrived at the party around 9:30 p.m. with a bouquet she had hoped to give to the rapper. During the evening, she and her friend spoke with Rahman while drinking at the bar.

At one point, Rivera was kicked out of the club for accidentally entering the men's rest room, police said. Rivera's friend said that around the same time, Rahman lured her to the roof by claiming Rivera was there.

When the friend rebuffed the suspect, he located the victim outside and "told her he could get her back in," Kelly said.

He took Rivera in through the employee entrance, then up to the roof in a service elevator, police said. Once there, he beat her inside a utility shed, killing her instantly, police said.

The man left the club at around 3 a.m., even though he was scheduled to work until 5 a.m., and went to Central Park and slept for a few hours, police said.

Police said that after Rivera's mother reported her missing on Tuesday, officers went to the club on Wednesday to review security videotape and do a floor-by-floor search of the five-story building. After they left, a repairman doing work at the club stumbled upon Rivera's body tucked away in the utility shed.

Officers found Rahman on Wednesday at an upper Manhattan apartment he shares with his parents.

A distraught Ingrid Estrada said Rivera, a customer service agent at John F. Kennedy International Airport for British Airways, was her only daughter whom she had raised as a single mother. She described her as "my life, my happiness."

Spotlight Live has become a popular tourist attraction by offering an "American Idol"-like experience. Guests perform with backup dancers and singers on a large stage, and the audience can vote for their favorite singers.

But it wasn't the first time the nightclub has seen trouble. In January, a 20-year-old Newark, N.J., man was stabbed to death after an argument inside spilled out onto the sidewalk and turned into a brawl. Five other men also were stabbed.

The club issued a statement expressing its condolences to the family of the victim.

"We are shocked by this terrible tragedy and our hearts go out to Ingrid Rivera's family and friends. We are grateful to the New York Police Department for arresting a suspect in this crime. We continue to cooperate with police and answer any questions they may have," the club said.

Lil' Kim's spokesman, Ronn Torossian, said in an e-mailed statement that Wednesday night was "the first (she) has heard of this matter." It's also unclear whether other celebrities were at the club at the time of the killing.

In July 2006, Lil' Kim got out of a federal detention center in Philadelphia after nearly 10 months behind bars for lying about a shootout outside a Manhattan hip-hop radio station. She was released early for good behavior.